Conventionally, JP 2011-1888 A (Reference 1) discloses a valve open/close timing control device which includes: a drive-side rotating body (“outer rotor” in Reference 1); a driven-side rotating body (“inner rotor” in Reference 1); a fluid pressure chamber which is partitioned into retarded angle chambers and advanced angle chambers by partition portions (“vanes” in Reference 1) which are formed by the drive-side rotating body and the driven-side rotating body, and are mounted on the driven-side rotating body; and a fluid control mechanism (“control valve” in Reference 1) which controls the supply of working fluid from a working fluid pump (“oil pump” or the like in Reference 1) which supplies working fluid to a fluid pressure chamber and the discharge of the working fluid from the fluid pressure chamber.
The valve open/close timing control device described in Reference 1 includes an intermediate phase fixing means which can fix a relative rotational phase of the driven-side rotating body with respect to the drive-side rotating body at a predetermined intermediate phase between a most retarded angle phase and a most advanced angle phase. The intermediate phase fixing means includes a locking key which is mounted on a drive-side rotating body side and a locking releasing hydraulic chamber formed in the driven-side rotating body, and the relative rotational phase is fixed at a predetermined intermediate phase due to the engagement of the locking key with the locking releasing hydraulic chamber.
Further, the valve open/close timing control device includes a stop-time phase change means which changes the relative rotational phase to the predetermined intermediate phase when a stop signal for stopping an internal combustion engine is detected. Accordingly, when the ignition is turned off, it is possible to stop the internal combustion engine after the relative rotational phase is fixed at the intermediate phase where the valve open/close timing is suitable for starting the internal combustion engine.
Due to such a constitution, the engine can be restarted in a state where the relative rotational phase is surely restrained to the predetermined phase. Accordingly, by setting the predetermined phase to a desired phase, the relationship between intake timing and ignition timing can be optimized so that startability of the engine can be enhanced. For example, it is possible to acquire a low-emission-type engine which emits a small amount of harmful combustion waste such as hydrogen carbide (HC).
Aiming at the enhancement of fuel economy, recently, the development of high compression in an engine has been in progress. In such an engine, a compression ratio becomes high when close timing of an intake valve is near a bottom dead center. Accordingly, there may be a case where the pre-ignition that the self-ignition of a mixture gas occurs before the ignition by an ignition plug arises under a condition that an intake air temperature is high. When the pre-ignition arises, a temperature of a cylinder wall is sharply elevated so that the lowering of an output or the malfunction of engine rotation is brought about. This may lead to the breaking of the engine. In such a case, the occurrence of the pre-ignition can be suppressed by lowering an actual compression ratio by changing closing timing to a retarded angle side using a variable valve timing mechanism. Accordingly, at the time of warm-starting the high compression engine, it is suitable to use a locking phase close to a most retarded angle side as the relative rotational phase of the valve open/close timing control device.
On the other hand, the engine is usually started using a starter (cell motor) in cold start, and a rotational speed of cranking in cold start is lower than a rotational speed of cranking in warm start and hence, in-cylinder pressure is hardly elevated. Accordingly, in cold start, an intermediate locking phase where the in-cylinder pressure is easily elevated is suitable as a relative rotational phase.
Further, the engine acquires an output by compressing air and fuel in the form of an air-fuel mixture and by igniting the air-fuel mixture. In an engine which repeatedly performs start and stop of the engine such as a hybrid engine or an engine which has an idling stop function, the vibrations of the engine in start can be suppressed by suppressing the compression of air. Accordingly, in restart of a hybrid engine in a warm state or in restart of the engine after an idling stop, a locking phase near a most retarded angle is suitable as a relative rotational phase.
In this manner, recently, along with popularization of hybrid engines and engines having an idling stop function, the number of phases suitable for starting an internal combustion engine is not limited to one phase. Further, also in an internal combustion engine having the constitution where a relative rotational phase is fixed at an intermediate phase and then the internal combustion engine is stopped when an ignition key is turned off, immediately after the ignition key is turned off, the supply of oil pressure is continued so as to change the relative rotational phase to the intermediate phase. Accordingly, the internal combustion engine is continuously operated for some time thus giving rise to a drawback from a viewpoint of fuel economy. Further, the fact that the internal combustion engine is continuously operated even after the ignition key is turned off gives a discomfort to a driver.
A need thus exists for a valve open/close timing control device which is not susceptible to the drawback mentioned above.